Stabilization of Gypseous Soil by Cutback Asphalt for Roads Construction

Numerous low- to medium volume roads constructed on gypseous soils, especially in the west and north parts in Iraq such as Al-Anbar & Salah-Al-din, encounter severe pavement cracking and premature loss of serviceability. The roads built on problematic Gypsum soils often become distressed due to volume changes associated with seasonal moisture content fluctuations. The objective of this paper is to study the effect of cut-back asphalt (MC-30) on the geotechnical properties of gypseous soil as stabilizing agent and investigate the ability of construct the road on this type of soil and obtain some mathematical models using SPSS program. The soil used in this study has been brought from Tikrit City at Salah-Al-din Governorate in Iraq with (34%) average gypsum content and classified as (SP) according to (USCS). A series of laboratory tests included physical, chemical, shear strength, collapsibility and stability tests are conducted on both untreated and treated soil samples with cut-back asphalt. Compacted soil samples with specification are prepared and five different percentage of cut-back asphalt are added to the soil samples and named as a binder content as (2, 4, 6, 8, and10) % and then tested. The results showed that using cut-back asphalt represents good solution and suitable alternative to improve the properties of gypseous soils by elimination the dissolving of gypsum when become in touch with water as well as increase in strength .....